Synthetic peptides have unique advantages compared with high molecular weight growth factor proteins. Phage display peptide libraries have enabled the discovery of peptides that selectively target specific organs but this technique has not been used to modulate bone repair. Using a phage display library in vivo, 13 peptide sequences have been identified by DMA sequencing. The sequences were detected repeatedly in phage that was isolated from bone and bone marrow. The goal of this project is to establish if the unique bone targeting peptides identified by in vivo biopanning of a phage display library will specifically bind to cells isolated form bone and bone marrow, and have the potential to modulate osteogenesis in vitro and bone regeneration in vivo. This study has 3 aims. In aim 1, the peptides that specifically bind to bone, and their putative receptors on bone or bone marrow cells will be identified. Three to four peptides showing specific binding to bone or bone marrow cells will be selected for further experiments. In aim 2, the effect of selected peptides on cells isolated from bone or bone marrow will be characterized in vitro. This includes the effect of peptides on adhesion, proliferation and/or differentiation of cells isolated from bone and bone marrow, and the effect of peptides on gene expression by these cells in a dose and time dependent manner. The most effective peptides will be selected for further study in vivo. In aim 3, the effect of selected peptides on promoting bone regeneration will be characterized in a rodent model. After developing a 3D-poly(lactide-co- glycolide) (PLAGA) delivery system, peptide related toxicity will be tested in rats by implanting the peptide- loaded PLAGA matrices subcutaneously. Then the peptides will be delivered into femoral defects in rats using 3D-PLAGA matrices and bone regeneration examined by histology, biochemistry, gene expression, micro-CT and biomechanics in order to elucidate details of peptide activity on bone regeneration. Further development of this approach can lead to the discovery of biologically active compounds that target bone and potentiate repair through mechanisms that are well characterized biologically at the cellular and molecualr levels. The observations would be expected have significant utility in the practice of Orthopaedic Surgery. [unreadable] [unreadable] [unreadable]